Basically, a characteristic of a control of driving force, speed change, steering or suspension is set to a predetermined characteristic. However, a driver of a vehicle changes occasionally, and driving environments such as a type of a road, a road surface condition and so on are varied widely while driving the vehicle. Therefore, it is preferable to change driving characteristics of a vehicle according to the driver's need. For this purpose, according to a conventional control system, the driving characteristic of the vehicle is changed by manually shifting a torque characteristic to a higher torque characteristic, or by changing a speed change map for controlling an automatic transmission. For example, the conventional control systems are configured to select a drive mode of the vehicle from a sporty mode where an agility of behavior of the vehicle is enhanced, a normal mode where the behavior of the vehicle is moderated in comparison with the sporty mode, and an economy mode where fuel economy is improved. However, each time the driver shifts the drive mode, the driver is required to operate a switch to select the driving mode. Such switching operation may bother the driver, and the shifting operation of the drive mode may be delayed by thus operating the switch.
In order to solve the above-explained disadvantages, according to the prior art, an intention of the driver has been attempted to be reflected on a vehicle control by judging the intention of the driver from a behavior of the vehicle. For example, Japanese Patent Laid-Open No. 10-272955 discloses a control system configured to calculate a sporty degree on the basis of lateral acceleration, a steering wheel angular velocity, a throttle opening, and a throttle opening/closing speed.
Meanwhile, Japanese Patent Laid-Open No. 2009-530166 discloses a control apparatus configured to judge a driving style of a driver. For this purpose, the control apparatus taught by Japanese Patent Laid-Open No. 2009-530166 is configured to calculate a so called “surface utilization” by weighting lateral acceleration and longitudinal acceleration individually to normalize those accelerations, and calculating the surface utilization on the basis of the normalized lateral acceleration and longitudinal acceleration. According to the teachings of Japanese Patent Laid-Open No. 2009-530166, such normalization is carried out to obtain a ratio of a detected acceleration to the maximum acceleration. Specifically, the surface utilization indicates a range of the longitudinal and lateral acceleration in which the vehicle may operate safely, and the surface utilization is obtained by squaring the normalized accelerations and adding together, and by obtaining a square root of the sum of those accelerations. Thus, according to the teachings of Japanese Patent Laid-Open No. 2009-530166, the surface utilization indicates a utilization of the area in which the vehicle may operate safely, that is, the driving style is indicated by the surface utilization.
Further, Japanese Patent Laid-Open No. 2004-257435 discloses a control device configured to determine sports driving intention of a driver. For this purpose, the control device taught by Japanese Patent Laid-Open No. 2004-257435 is configured to change a speed change schedule, in case a vehicle acceleration integrated value of exceeds a reference value and an existence of the sports driving intention is thereby judged.
In addition, according to the teachings of Japanese Patent Laid-Open No. 2004-257435, a determination of an existence of the sports driving intention is facilitated by reducing the reference value, in case a running resistance is large. Further, Japanese Patent Laid-Open No. 2007-536479 discloses another method for controlling a transmission by carrying out the weighting. Specifically, the method taught by Japanese Patent Laid-Open No. 2007-536479 is configured to optimize a shifting process depending on a type of a vehicle and a driving condition. For this purpose, according to the teachings of Japanese Patent Laid-Open No. 2007-536479, an input variable influencing the shifting operation is normalized and weighted.
Basically, the driving condition of the vehicle is changed depending on a driving environment such as a road condition, and also changed by an execution of unexpected operation out of the driver's habit. In addition, the driving condition of the vehicle is also changed by a temporal operation for avoiding some sort of obstacle. However, according to the teachings of Japanese Patent Laid-Open No. 10-272955, the control system is configured to calculate the sporty degree while reflecting the above-mentioned driving environment and specific factors. Therefore, the sporty degree may not be calculated accurately.
As described, the control apparatus taught by Japanese Patent Laid-Open No. 2009-530166 is configured to carry out the weighting to obtain a ratio of the detected acceleration to the maximum acceleration. That is, in case the detected acceleration is deviated from the driver's intention by a driving condition of the vehicle, or in case a relation therebetween is being changed according to the driving condition of the vehicle, the driving style may not be judged accurately.
As also described, the control device taught by Japanese Patent Laid-Open No. 2004-257435 is configured to change the reference value for determining the sports driving intention according to the running resistance. Therefore, in case the running resistance is changed irrespective of manual operations, the determination of the sports driving intention may be satisfied or dissatisfied alternately by such change in the running resistance. In this case, control content may be altered by such alternation of the judgment, and as a result, the speed change schedule may be changed without carrying out any specific manual operation. Therefore, the driver may feel uncomfortable feeling. That is, although the control device is configured to reflect the driver's intention on the driving condition, the control device thus configured may change the driving condition of the vehicle regardless of the driver's intention.